In recent years, attention has been given to the function of oligosaccharides and glycoconjugates in living bodies. For example, a determinant factor of a blood type is a glycoprotein, and one involved in the function of the nervous system is a glycolipid. Thus, an enzyme having the function of synthesizing an oligosaccharide is a crucially important key for analyzing physiological activities produced by various oligosaccharides.
A N-acetyl-D-glucosamine residue (GlcNAc) and a D-galactose residue (Gal), and the like, in sugar are the components of glycosaminoglycan, while they are sugar residues present in various oligosaccharide structures such as sphingoglycolipids, mucin-type oligosaccharides, and asparagine-linked oligosaccharides (N-linked oligosaccharides). Thus, an enzyme transferring GlcNAc or Gal is a crucially important tool for analyzing the function of oligosaccharides that work in various tissues in living bodies.
For example, at least 20 types of N-acetylglucosaminyltransferases having an activity of transferring GlcNAc have been known as shown in Table 1, each of which differs in acceptor substrate specificity (References 1 to 18).
On the other hand, oligosaccharide synthesis is known to be altered with great frequency in canceration and to be correlated with the metastasis and malignancy of cancer (References 30 to 32). Their comprehensive studies actively conducted today, for example, analysis such as expression profiling in a variety of tissues, are also directed to the elucidation of a canceration mechanism, and discussions have often been conducted on the possibility that the canceration mechanism is associated with the expression level of a particular gene. As well known, the test of tumor markers or the like in blood and the identification of the other gene products involved in canceration, and so on, have already been conducted as methods of cancer diagnostic tests. Tumor markers include many antibodies against oligosaccharides. Among others, immunoassay for oncogene products has often been adopted because of its advantage in high sensitivity.
TABLE 1N-acetylglucosaminyltransferases and their substrate specificityAbbrevi-LinkageOfficial nameationtypeSubstrate specifictyReferenceN-acetylglucosamlnyltransferase-IGnT-Iβ1-2Manα1-3␣Manα1-6)Manα1-6(Manα1-3)Manβ1-14GlcNAcβ1-4G3cNAcβ1-AsnN-acetylglucosamlnyltransferase-IIGnT-IIβ1-2Manα1-6(GlcNacβ1-2Manα1-3)Manβ1-4GlcNAcβ1-Asn2N-acetylglucosamlnyltransferase-IIIGnT-IIIβ1-4GlcNAcβ1-2Manα1-6(GlcNAcβ1-2Manα1-3)Manβ1-4GlcNAc3β1-4G3cNAcβ1-AsnN-acetylglucosamlnyltransferase-IVGnT-IVβ1-4GlcNAcβ1-2(GlcNAcβ1-6)Manα1-6(GlcNAcβ1-2Manα1-3)4Manβ1-4GlcNAcβ1-4G3cNAcβ1-AsnN-acetylglucosamlnyltransferase-VGnT-Vβ1-6GlcNAcβ1-2Manα1-6(GlcNAcβ1-2(GlcNAcβ1-4)Manα1-3)5Manβ1-4GlcNAcβ1-4G3cNAcβ1-AsnN-acetylglucosamlnyltransferase-VIGnT-VIβ1-4GlcNAcβ1-2(GlcNAcβ1-6)Manα1-6(GlcNAcβ1-2)(GlcNAcβ1-4)6Manα1-3)Manβ1-4GlcNAcβ1-4G3cNAcβ1-Asnβ1,3-N-acetylglucosamlnyltransferaseIGnTβ1-3Galβ1-4GlcNAcβ1-R7β1,3-N-acetylglucosamlnyltransferase-2β3GnT2β1-3Galβ1-4GlcNAcβ1-R8β1,3-N-acetylglucosamlnyltransferase-3β3GnT3β1-3Galβ1-3GalNAc-O-S/T8β1,3-N-acetylglucosamlnyltransferase-4β3GnT4β1-3Galβ1-4(GlcNAcβ1-3Gal β1-4) n-R8β1,3-N-acetylglucosamlnyltransferase-5β3GnT5β1-3Galβ1-4GlcNAcβ1-3Gal β1-4-Cer9β1,3-N-acetylglucosamlnyltransferase-6β3GnT6β1-3GalNAc-O-S/T10β1,3-N-acetylglucosamlnyltransferase-7β3GnT7β1-3Galβ1-4(GlcNAcβ1-3Gal β1-4-Cer11β1,3-N-acetylglucosamlnyltransferaseFringeβ1-3C2-X-X-G-G-(Fuc-O) S/T-C312β1,6-N-acetylglucosamlnyltransferaseIGnTβ1-6GlcNAcβ1-3Galβ1-4GlcNAcβ1-R13Core 2 β1,6-N-acetylglucosamlnyl-C2GnT-Iβ1-6Galβ1-3GalNAc-O-S/T14transferase-ICore 2 β1,6-N-acetylglucosamlnyl-C2GnT-IIβ1-6Galβ1-3GalNAc-O-S/T15transferase-IICore 2 β1,8-N-acetylglucosamlnyl-C2GnT-IIIβ1-6Galβ1-3GalNAc-O-S/T16transferase-IIIα 1,4-N-acetylglucosmlnyltransferaseα 4GnTα 1-4Galβ1-3(Galβ1-4GlcNAcβ1-6)GalNAc-R17peptide β-N-acetylglucosamlnyl-OGTO-Y-S-D-S-P-S-T-S-T18transferaseTransferring N-acetylglucosamine to an underlined sugar or amino acid.
TABLE 2References1J Biol Chem. 10: 250 (9): 3303-9 (1975)2Can J Biochem Cell Biol. 61 (9): 1049-66. (1983)3J Biol Chem. 10: 257 (17): 10235-42. (1982)4J Biol Chem. 25: 258 (10): 6162-73. (1983)5J Biol Chem. 25: 257 (22): 13421-7. (1982)6J Biol Chem. 20: 275 (42): 32598-602. (2000)7Cell 105: 957-69 (2001)8J. Biol. Chem. 276 (5). 3498-507 (2001)9J Biol Chem. 276: 22032-40. (2001)10J Biol Chem. 12: 277 (15): 12802-9. (2002)11Biochem. Biophys. Res. Commun. 294 (4). 843-8 (2002)12Nature 406: 411-5 (2000)13J. Biol. Chem. 259: 13385-90 (1984)14J. Biol. Chem. 255: 11253-61 (1980)15J. Biol. Chem. 274: 3215-21 (1999)16J. Biol. Chem. 275: 11106-13 (2000)17Proc. Natl. Acad. Sci. U.S.A. 96, 8991-6 (1999)18J. Biol. Chem. 265: 2563-2568 (1990)References    Reference 30: Kobata A., Eur. J. Biochem. 15, 209(2), 483-501, 1992    Reference 31: Santer U. V. et al., Cancer Res., September 44(9), 3730-5, 1984    Reference 32: Taniguchi N., Biochem. Biophys. Acta., 1455(2-3), 287-300, 1999
As described above, the identification of gene products having some involvement in canceration is expected to provide tumor markers useful in cancer diagnosis. If especially a nucleic acid found in a transcript can be used as an indicator for testing canceration, only the identification of a transcript of a particular gene can sufficiently provide an indicator useful in testing canceration, without the need for elucidating the function of its end product, for example, a protein. Especially the identification of a nucleic acid has advantages which are not found in immunoassay, because it can be performed on a DNA microarray and a nucleic acid even in small amounts can also be quantified after being amplified by PCR.
On the other hand, the function of oligosaccharides in living bodies receives attention. However, the analysis of oligosaccharide synthesis in living bodies does not necessarily progress satisfactorily. This is partly because the mechanism of oligosaccharide synthesis and the localization of sugar synthesis in living bodies are not sufficiently elucidated. The analysis of the mechanism of oligosaccharide synthesis requires the analysis of enzymes synthesizing oligosaccharides, especially glycosyltransferases, and analyzing which type of oligosaccharide is generated with the enzyme. Therefore, there also has been a growing demand for finding a novel glycosyltransferase and analyzing its function.